1. Field of the Invention
The present invention relates to a gas turbine apparatus, and more particularly to a gas turbine apparatus having a control system for controlling electric power generated by an electric generator based on the temperature of a discharged combustion gas. The present invention also relates to a method of controlling electric power generated by an electric generator in a gas turbine apparatus.
2. Description of the Related Art
Generally, a gas turbine apparatus has a turbine which is rotated by a fluid applied to the turbine, a combustor for combusting a mixture of fuel and air, a fuel flow control valve for adjusting the amount of fuel to be supplied to the combustor, and an air compressor for compressing air and supplying the compressed air to the combustor. The combustor produces a combustion gas having a high temperature and a high pressure when the mixture of fuel and air is combusted in the combustor. The combustion gas is supplied to the turbine to rotate the turbine at a high rotational speed.
The gas turbine apparatus has a PID processing unit for controlling the rotational speed of the turbine. The PID processing unit adjusts the amount of fuel to be supplied through the fuel flow control valve to the combustor to rotate the turbine at a constant rotational speed. In order to bring the present rotational speed into a desired rotational speed, the PID processing unit performs a feedback control process. Specifically, the rotational speed of the turbine is fed back to the PID processing unit, which calculates an optimal amount of fuel to be supplied to the combustor so as to minimize a deviation between the present rotational speed and the desired rotational speed. The PID processing unit calculates the amount of fuel to be supplied according to a PID control process.
A PID control process is employed to bring the present value of a controlled system into a predetermined set point. In such a PID control process, a manipulated variable (control output value) to eliminate a deviation between the present value and the set point is calculated based on a proportional action, an integral action, and a derivative action. Thus, “PID” stands for a combination of the initials of the proportional action, the integral action, and the derivative action. According to a PID control process, a system can be controlled by a combination of a proportional action corresponding to a magnitude of a deviation, an integral action corresponding to a period of time for which the deviation continues, and a derivative action corresponding to a change in the deviation.
Generally, when a gas turbine apparatus starts to operate, a large amount of fuel is supplied to a combustor in order to rapidly increase the rotational speed of a turbine to a rated rotational speed. Accordingly, a mixture of fuel and air is vigorously combusted. A combustion gas produced by the combustor directly affects the temperature of the gas turbine apparatus, particularly the temperatures of the combustor and a regenerator (heat exchanger) provided near a discharge port of the turbine. Thus, the temperature of the gas turbine apparatus may excessively be increased when the gas turbine apparatus starts to operate. Therefore, the gas turbine apparatus has a PID processing unit for controlling the amount of fuel to be supplied so that the temperature of the discharged combustion gas is maintained at temperatures lower than a predetermined temperature. The PID processing unit is arranged to operate after the mixture of fuel and air is ignited until the rotational speed of the turbine reaches the rated rotational speed.
There has been known a gas turbine apparatus having an electric generator coupled to a rotational shaft of a turbine so that the electric generator is driven by the turbine to generate electric power. Generally, the amount of fuel to be supplied should be increased in order to increase electric power generated by the electric generator. In such a case, the temperature of the gas turbine apparatus is also increased. In order to prevent the temperature of the gas turbine apparatus from being increased to an extremely high temperature, it is necessary to control electric power generated by the electric. generator. The conventional gas turbine apparatus employs a dedicated control logic to control generated electric power and thus requires a complicated circuit arrangement in a control system of the apparatus.